What Should I Do if I Put the Wrong Fuel in My Car?
- Car ownership
Putting the wrong type of fuel in your car can be a costly mistake, but there are some things you can do to limit the damage.
Book a car repair nowEllie Dyer-Brown
Thursday February 15 2024
5 min read
Putting petrol in a diesel car, or the other way around, is a surprisingly easy mistake to make. According to the RAC, around 150,000 people accidentally put the wrong fuel in their car each year.
Because diesel has a wider nozzle that's harder to fit into a petrol car, 95% of misfuelling happens when petrol is put into a diesel car. That’s what we’re going to focus on in this guide.
In a nutshell: The most important thing to remember about misfuelling is that you shouldn't start the engine with the wrong fuel in the tank. Instead, call your breakdown recovery provider and get the fuel system drained.
How far can you drive with petrol in a diesel car?
The better question to ask would be should you drive with petrol in a diesel car, and the answer is a definite “no".
As soon as you start the engine, the damage will begin, and it’s not just limited to one area. It isn’t possible to drive a diesel car using petrol.
Your car might work for a short while, but after that you’ll need to pay for expensive repairs. The best thing to do is double check which pump you've grabbed before you start filling up.
What to do when you put petrol in a diesel car
Putting petrol in a diesel car can cause more damage than putting diesel in a petrol. If this does happen, don’t fret – you can do damage limitation if you realise you’ve used the wrong fuel before you start the engine.
All you have to do is call your breakdown provider or mobile mechanic and they’ll get it sorted.
Then it's just a case of draining your tank and refilling it with the correct fuel. If you spot your mistake quickly, you should be okay, as it’s commonly agreed that you can mix up to 5% diesel in a petrol tank without breaking your car or the bank.
The real damage happens when you start the car and drive away. As soon as you turn the key in the ignition and the dashboard lights up, your fuel pump has come to life. The engine is supposed to be primed with diesel before it starts, but when you accidentally put petrol in it, it will be sucking the offending liquid into the fuel lines. So, not only will your tank then need to be drained, your fuel pipes will need to be flushed as well – which isn’t cheap.
What are the symptoms of putting petrol in a diesel car?
Thick black smoke.
Engine cutting out.
Engine starting to cough or chug.
An unusual smell.
Use this guide to diagnose car problems and find the right fix.
What’s the worst case scenario when you put petrol in a diesel car?
As we mentioned earlier, sticking your key in the ignition is the worst thing you can do. If your engine starts, you’re in for some real trouble.
This is because a modern diesel engine utilises different types of technology to save mpg figures and minimise emissions. The fuel pumps are greased with diesel as it passes through.
When petrol enters these diesel pipes, rather than lubricating the tubes, its solvent properties create internal friction. The metal surfaces grind together, which causes them to disintegrate, and create a swarf. Microscopic particles of metal could be created, causing further damage to your car’s engine.
After the petrol has gone through the pumps, the engine’s high-pressure injectors are the next thing to go. They force fuel through the engine’s cylinders via incredibly fine holes with an engineered spray pattern. If this swarf gets into the injection system, it will block some or all of the holes. This really is the worst case scenario as a common rail injector system could cost thousands of pounds to replace.
If you think you’ve put the wrong fuel in your car then find and call a local garage or breakdown service to get it fixed as soon as possible.
What’s worse, diesel in a petrol car or petrol in a diesel car?
Putting petrol in a diesel car is considerably worse than making the mistake the other way around.
If you put diesel in a petrol car, the engine will run on lower power and there will be lots of smoke. The fuel can be drained from the tank and replaced, usually without any long term problems.
On the other hand, running a diesel engine on petrol could cause significant damage. If you realise you’ve put petrol in your car incorrectly, don’t start the engine, push the car to a safe place and wait for assistance from a professional.
How to tell the difference between petrol and diesel
Petrol and diesel both have distinct smells which can be used to identify them. The latter fuel is a lot thicker and black in colour, whereas petrol can be light red and light green.
Similarly, petrol fuel pumps are colour coordinated, with black for diesel and green for petrol.
Is my car diesel or petrol?
If you need to work out what type of fuel a particular car needs, the fuel cap label should indicate this. You can also tell by sound; diesel engines make a louder, harsher noise compared to the generally smoother sound of a petrol car. Failing that, consult your owners manual.
Have you filled up your car with the wrong fuel? Don't panic - FixMyCar's trusted garage network can help.
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Written by Ellie
Ellie is FixMyCar's Content Writer. She has over three years of experience writing about cars and regularly collaborates with automotive experts to provide trustworthy advice for drivers that is easy understand. Her work has been featured in Yahoo! Finance, iNews, The Daily Express and The Sun. She has a BA in English literature and an MA in creative writing from Durham University. Outside of work, Ellie follows F1 and eagerly awaits Ferrari's next era of dominance in the sport. She drives a Suzuki Swift.